Field of the Invention
The invention relates to the operation of an inductive power transfer (IPT) system. The invention includes (i) a method of detecting an arrangement, (ii) a method of operating an IPT system comprising the method of detecting the arrangement, (iii) a primary unit arrangement of an IPT system and (iv) a secondary unit arrangement of an IPT system.
The IPT system comprises a primary (side) unit with a primary winding structure, which primary unit is located in particular on a route or on a stop (e.g. a bus stop or parking area) of a vehicle which can drive along the route. The primary winding structure generates a magnetic field which is received by a secondary (side) unit of the IPT system that is also known as receiver or pick-up. In case of a vehicle, it may be related to as on-board receiving unit (ORU). The secondary unit has a secondary winding structure. The primary and secondary winding structures comprise windings of in each case at least one electric conductor. In between the primary winding structure and the secondary winding structure, there is an air gap through which the generated electromagnetic field extends during operation. An electric voltage is induced in the secondary winding structure and, while the secondary unit provides power to any load, the load current through the secondary winding structure generates a secondary electromagnetic field. This current depends at least partially on the mutual induction between the primary winding structure and the secondary winding structure. The primary unit and the secondary unit form an electrical transformer.
Description of Related Art
The IPT system can be used for static energy transfer or static charging of a vehicle, i.e. the vehicle does not move during energy transfer. In this case, the primary unit can be designed as a so-called charging pad, which may be integrated into the route or mounted on the route surface as an elevated charging pad. Alternatively, the IPT system can be a dynamic system transferring energy while the vehicle travels along the driving surface of the route.
WO 2014/095722 A2 discloses a safety system for an inductive power transfer system that transfers power to a vehicle on a surface of a route, wherein the safety system comprises at least one inductive sensing system, wherein the inductive sensing system comprises multiple detection windings and wherein the multiple detection windings are arranged in an array structure, which at least partially covers a charging surface that is assigned to the primary winding. The safety system detects foreign objects, in particular metal objects, located in proximity of the primary winding structure.
The primary unit and the secondary unit of the IPT system comprise electrically conductive parts, at least the windings mentioned above. Typically, they also comprise magnetic or magnetizable material, in particular ferrites, for shaping the magnetic field of the IPT system during operation. Since there is an air gap between the primary unit and the secondary unit, the units are movable relative to each other. Therefore, a vehicle having an on-board secondary unit can move to a predetermined position where the energy transfer from the primary unit to the secondary unit is optimal. Consequently, there is a need to ensure that the secondary unit is actually in the optimal position. For example, mechanical means may be provided for this purpose. Another option is a control device which controls positioning the vehicle based on contactless detecting the relative position of the primary and secondary unit.
The same primary unit may be used to provide energy to different vehicles one after the other. For different reasons, there is a need to detect or recognize which vehicle or which type of secondary unit is actually positioned close to the primary unit. One possible reason is that the billing for the energy delivered must be directed to the correct address. Another possible reason is that there may be different types of secondary units and that the primary unit may be operated in a different manner depending on the type of the secondary unit which is to be provided with energy.
Another aspect of operating an IPT system is the detection of undesired, foreign objects which are not part of the IPT system. According to WO 2014/095722 A2, a safety system is provided for this purpose. In particular, if the foreign object is electrically conductive, it can be heated up rapidly, thereby becoming a dangerous hot object. In addition, the foreign object may deteriorate the energy transfer to the secondary unit.